PROJECT SUMMARY The development of a functional organ system during embryogenesis not only requires that cells adopt an appropriate cell identity and pattern, but also the ability to maintain this identity and morphology in the face of ongoing genetic and environmental perturbations that occur throughout embryogenesis. This ability to recover from potentially disruptive alterations in development is referred to as plasticity or regulative ability. While all cells possess some degree of plasticity in order to adapt to adverse conditions, pronounced plasticity is feature of embryos. While there has been enormous progress in elucidating the molecular-cellular processes governing normal development, there has been relatively less focus on elucidating the mechanisms governing the extended process of regulation following a developmental perturbation, despite its clear importance for a comprehensive understanding of development as well as its implications for regenerative medicine. Here we employ the classic amphibian embryological system of Xenopus laevis to examine the regulative ability of the presumptive nervous system during early embryogenesis. Previous experiments from our lab have demonstrated that when the presumptive neural plate is removed from a mid-gastrula-stage embryo, rotated 180o, and transplanted back into a host embryo from which the equivalent region was removed, there is a near total recovery, with the resulting embryo giving rise to a nervous system with appropriate regional gene expression and functional capabilities. This regulative ability diminishes considerably by late gastrula stages. In an effort to determine the molecular basis of this early developmental plasticity, we conducted a global gene expression, RNA-Seq experiment on control embryos and embryos with rotated neural tissue. Our RNA-Seq data suggest a model in which specific aspects of early neural plasticity are associated with a unique signature of pathways and genes. The ability for transplanted tissue to incorporate and heal entails the upregulation of apoptosis, ubiquitination, and oxidative stress, and specific ion flux pathways while the ability to recover from rotation of neural tissue and re-patterns the anterior-posterior axis involves calcium homeostasis, chromatin remodeling, neuronal transcription factor, and recognition molecule genes. In our first specific aim we will obtain the temporal and spatial mRNA expression profiles of genes identified from RNA-Seq data to determine if their expression patterns are consistent with a role for mediating specific aspects of early neural plasticity. Our second aim will determine whether the candidate genes?whose expression patterns are consistent with playing a role in early embryonic plasticity?functionally mediate regulative behavior of early neural tissue by conducting gene knock-out/knockdown and overexpression assays. Taken together these data will provide new insights into the plasticity and regulative behavior of the early embryonic nervous system that may have important implications for understanding a fundamental and near universal feature of embryos as well as for regenerative medicine.